1. Field of the Invention
The present invention relates to a light source apparatus and a laser scanning microscope.
This application is based on Japanese Patent Applications, Nos. 2007-304896 and 2008-266551, the content of which is incorporated herein by reference.
2. Description of Related Art
A light source apparatus has been known in the past, which includes a laser diode generating repetitive pulse light (for example, refer to a specification of the Publication of Japanese Patent NO. 2777268).
The light source apparatus includes a lock-in amplifier, and is intended to provide a high speed pulse with low noise by providing a peak in frequency of a reference signal for the lock-in amplifier.
However, when the lock-in amplifier is in use, the reference signal needs to have a frequency, and therefore when light having certain light quantity is continuously emitted, there is a problem in that the quantity of light cannot be stabilized. Moreover, when the lock-in amplifier is in use, there is a problem in that a light source apparatus becomes expensive.
On the other hand, in some method, feedback of light is made using a detector such as photodiode in order to stabilize the quantity of light. However, when light modulated at high frequency is detected and fed back, there is a problem in that response speed of a feedback circuit cannot follow modulation speed of the light due to floating capacitance or high feedback gain of the feedback circuit.
Therefore, when both of highly stable light and fast-modulated light are emitted, even if light having the same wavelength are emitted, separate laser diodes are required.
When a laser diode is in use at a low power, a photodiode incorporated in the laser diode may be reduced in response speed (much time may be taken before the photodiode is stabilized) in some photodiode type. Therefore, when a feedback circuit is configured, there is a problem in that actual output value overshoots a target output value given by a lighting instruction signal.
Therefore, even when laser light is modulated at low frequency, when feedback of light is made using a detector-such as photodiode, stability of the light may be reduced in some lighting power.